1. Field of the Invention
This invention relates to semiconductor packaging technology, and more particularly, to a ball grid array (BGA) semiconductor package and method of fabricating the same, which can be used for the fabrication of a BGA package, and which can help prevent the fabricated BGA package from having voids in the package body thereof to thereby ensure the quality of the BGA package.
2. Description of Related Art
BGA (Ball Grid Array) is an advanced type of semiconductor packaging technology which is characterized by the use of a substrate as chip carrier whose front side is used for mounting one or more semiconductor chips and whose back side is provided with a grid array of solder balls. During SMT (Surface Mount Technology) process, the BGA package can be mechanically bonded and electrically coupled to an external printed circuit board (PCB) by means of these solder balls.
FIG. 1A and FIG. 1B respectively show a sectional view and a top view of a conventional BGA package. As shown, this BGA package comprises: (a) a substrate 10; (b) a ground pad 20; (c) a solder mask 30; (d) a semiconductor chip 40; (e) an electrically-conductive layer (such as silver paste) 50; (f) a set of bonding wires (such as gold wires) 60; (g) an encapsulation body 70; (h) a plurality of electrically-conductive vias, including a group of ground/heat-dissipation vias 81 and a group of power/signal vias 82; and (i) a grid array of solder balls, including a group of ground/heat-dissipation balls 91 and a group of power/signal vias 92.
The chip 40 is electrically coupled to the ground/heat-dissipation balls 91 successively by way of the silver paste layer 50, the ground pad 20, and the ground/heat-dissipation vias 81, so as to be electrically coupled to the ground/heat-dissipation structure on an external printed circuit board (not shown) by way of the ground/heat-dissipation vias 81.
One drawback to the foregoing BGA package, however, is that voids 51 would exist in the silver paste layer 50 filled in the opening 31 of the solder mask 30, which would undesirably cause a popcorn effect during subsequent reflow process under a high temperature condition. This popcorn effect would break apart the encapsulation body, causing the BGA package to become defective.
The cause of the existence of the voids 51 is depicted in FIGS. 2A-2C. As shown in FIG. 2A, during the die-attachment process, an adhesive agent, such as silver paste, is coated over the surface of the solder mask 30 to form the silver paste layer 50; and then as shown in FIG. 2B and FIG. 2C, the chip 40 is forcefully pressed down against the silver paste layer 50, thus urging the silver paste layer 50 to spread out over the die-attachment area. During this process, however, since the overall width of the chip 40 is located directly above the opening 31 in the solder mask 30, it would undesirably trap the air in the opening 31, thus resulting in the forming of voids 51 therein. The existence of these voids 51 would undesirably cause a popcorn effect during subsequent reflow process under a high temperature condition. This popcorn effect would break apart the encapsulation body, causing the BGA package to become defective.
Related patents includes, for example, the following patents:
U.S. Pat. No. 5,545,923 xe2x80x9cSEMICONDUCTOR DEVICE ASSEMBLY WITH MINIMIZED BOND FINGER CONNECTIONSxe2x80x9d;
U.S. Pat. No. 5,703,402 xe2x80x9cOUTPUT MAPPING OF DIE PAD BONDS IN A BALL GRID ARRAYxe2x80x9d.
The foregoing patents, however, provide no solutions to the aforementioned problem, and therefore it cannot be used to eliminate the popcorn effect to help ensure the quality of the BGA package. There exists therefore a need in the semiconductor industry for a new semiconductor packaging technology that can eliminate the popcorn effect due to existence of voids in the BGA package.
It is therefore an objective of this invention to provide a new BGA semiconductor packaging technology that can eliminate the popcorn effect due to existence of voids in the BGA package.
The BGA semiconductor packaging technology according to the invention comprises the following steps: preparing a substrate having a predefined die-attachment area on one surface thereof; (2) forming a ground pad over the die-attachment area on the substrate; (3) forming a solder mask over the ground pad, wherein the solder mask is formed with at least one opening to expose one portion of the ground pad, and wherein the opening is located in such a manner that a fraction of the overall width of the opening is located beyond the die-attachment area; (4) pasting an adhesive agent over the solder mask; and (5) pressing at least one semiconductor chip forcefully against the adhesive agent over the solder mask, causing the adhesive agent over the solder mask to spread out sideways and fill into the opening in the solder mask to expel the air in the opening through the gap above the opening to the atmosphere.
The BGA semiconductor packaging technology according to the invention is characterized in that openings of a solder mask are formed on a given edge of a die attachment area, and entire or partial width of each opening is disposed outside the die attachment area. Accordingly, air within the opening of the solder mask is sufficiently eliminated during die bonding process, so as to prevent void formation as adhesive is filled into the opening. Therefore, in the follow-up steps, high temperature in reflowing process will not cause popcorn as in the prior-art, so as to remain good quality of the semiconductor package.